This invention generally relates to antennas. More specifically, this invention relates to an antenna coupled with a parasitic element.
As the technology for cellular telephones advances, more operating modes and operating frequency bands are becoming available. Making a cellular telephone operable for all of these modes and at all of these frequencies places great demands on the performance of cellular telephone antenna system. In particular, multi-mode and multi-band cellular systems are demanding greater operation bandwidths for antenna systems. Short helical antennas and other small antennas have too narrow of a band of operation to cover the spectrum required of multi-band telephones, particularly when the antenna is coupled with conductive surfaces or planes in proximity to the antenna.
One solution for providing increased bandwidth is to provide a larger antenna element. However, the demand is for smaller sized telephones which makes this solution impractical. Another solution is to reduce the efficiency of the antenna. However, the efficiency of the cellular telephone antenna significantly impacts the amount of energy needed to send and receive signals. If an antenna is inefficient, the power amplifier of a cellular telephone has to produce a higher power signal to overcome the inefficiency of the antenna, which undesirably shortens battery life. Moreover, on the receive side of operation, the sensitivity of the cellular telephone is impacted by the efficiency of the antenna.
Furthermore, cellular telephones are increasingly designed to operate via more than one frequency band. An antenna system can be required to operate from a lower frequency band of operation of about 800 MHz up to a higher frequency band of operation of 2 GHz or more. This places great demands on antenna systems and is difficult to accomplish with conventionally.
Therefore, there is a need for an improved antenna system that is operable at multiple frequency bands without impacting antenna efficiency. There is a further need for an efficient antenna structure with a bandwidth large enough to operate efficiently over the required cellular frequency bands of operation.